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World's largest volcano identified off coast of Japan

Scientists recently discovered that Tamu Massif, an underwater volcano that measures more than 120,000-square miles, is a single shield volcano. It is the largest on Earth, and among the largest in the entire solar system.

Located about 1,000 miles off the coast of Japan, the base of this Pacific Ocean volcano is about four miles below sea level, though scientists believe it was just below the surface as it formed some 145 million year ago. University of Houston professor William Sager has been studying the underwater mountain range for more than 20 years, but could only recently designate Tamu Massif as a single volcano. His research is published in the current issue of the journal Nature Geoscience.

Previously, it was debated whether Tamu Massif was a complex of volcanoes or one single volcano. An example of a volcano complex is Hawaii's Big Island, which features four volcanoes.

Before the discovery of Tamu Massif, Hawaii's Mauna Loa was considered the largest active volcano on Earth. But Mauna Loa's 2,000 sqaure miles pale in comparison to Tamu Massif's 120,000. Another volcano in the same range as Tamu Massif is also massive -- about 30,000 square miles, according to Sager, but scientists need to study Ori Massif further before they can definitively say if it is an individual volcano or a complex.

Tamu is named for Texas A&M University, where Sager was working when he first started studying the mountain range, he told Other mountains in the range are named for Japanese and Russian research facilities that were collaborating with Texas A&M at the time.

"This mountain range had been known for generations, and we knew there was this big mountain mass there," Sager said. "The new thing here is that we didn't know anything about its structure, we didn't have seismic gear that could penetrate it."

Sager said their best guess was always that Tamu Massif was a complex of volcanoes. But in 2009, his team set out to study the volcano using the tools aboard the Marcus G. Langseth, a one-of-a-kind research vessel equipped with seismic imaging gear. "The ship is our version of a space telescope," Sager said.

If it was a complex, the lava flows on Tamu Massif would have pointed to multiple centers. But that wasn't what they saw.

"The patterns went up flanks to center," Sager recalls. "That's when we realized this is really one big volcano."

The team also drilled 170-meters into the flank of the volcano.

"It's like pin-pricking the elephant," says Sager. "We analyzed the lava flows, which were as much as 75 feet thick, and were also able to take that information and match it to the seismic images."

Samples taken from the top of the volcano indicate that it once sat in shallow water, but never quite rose above sea level. They believe the volcano formed over the course of one to two million years.

Further research is needed to understand why it never reached above sea level.

"It formed on a series of mid open ridges, like Iceland," said Sager. Iceland rose above sea level because it was pushed up by the broad swell of hot material, or magna, that sits beneath it, he explained.

"We would've thought the same thing would happened here. We were thinking it must've been sticking up but there's no smoking gun, no evidence that it ever stuck up. It's tantalizing because it should've been. There's something important that we need to understand."

Continued research could also show that there are still dead volcanoes even larger than Tamu Massif, he added. "This isn't the biggest oceanic plateau. We just don't know the structure of the inside of the Ontong Java Plateau yet. We expect it's a complex of volcanoes, but it could be just one. And then that would be the biggest."

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